Dependence on Geomagnetic Activity of Magnetic Pulsation Frequency of pc-3 and pc-4 Ranges

Abstract

Summary Frequency spectra of magnetic pulsations of frequency range from 5 to 100 mHz observed at temperate latitudes consist of two dominant frequency bands, 15 mHz and 35 mHz in their representative average values. The frequency of both bands increases with an increase of geomagnetic activity represented by Kp or Kp. The time of occurrence of maximum frequency in both bands in their regular daily variation of frequency advances towards the dawn side with an increase of Kp It seems likely that the resonators for the 15 mHz and 35 mHz bands can be identified respectively to a standing Alfven wave along the field line on the plasmapause and a standing modified Alfven wave between the plasmapause and the ionosphere. Then, the increase in frequency and the dawnward shift of maximum frequency time can be ascribed to a contraction and a deformation, respectively, of the plasmapause caused by an intensified solar wind accompanied by an increase in Kp-index.